1. Field of the Invention
The present invention relates to a printing apparatus.
2. Description of the Related Art
Printing apparatuses that print information such as text and images on a printing medium are known in the art. Among these is known, for example, a printing apparatus that employs an inkjet printing method for printing using ink. Such a printing apparatus is provided, for example, with a printhead for printing utilizing thermal energy (see Japanese Patent Laid-Open No. 11-115173).
FIG. 11 illustrates an example of the general configuration of a printing apparatus 100 according to the prior art. The printing apparatus 100 is provided with a power supply circuit 101, printhead 102, control circuit 103 and motor 104.
The printhead 102 is provided with one or a plurality of nozzles (orifices) and with a heater for each corresponding nozzle. When voltage is applied to the heater, ink is discharged from the nozzle.
The control circuit 103 generates an image signal [data (a discharge image signal) in a form made to conform to the nozzles of the printhead 102, and a discharge control signal (heating pulse) for controlling the heaters] and transfers the image signal to the printhead 102.
The power supply circuit 101 supplies power to each of these components. The power supply circuit 101 supplies the components with power (VCC) for operating logic circuitry, motor driving power (VM) and head driving power (VH), by way of example. Since the voltage of VH is high in comparison with the voltage of VCC, some time is required for the optimum voltage (a predetermined voltage) to be attained. For this reason, generally voltage is applied to the heaters in synch with mechanical control that precedes discharge of ink. Further, control of the heating pulses is exercised independently of control of VH.
On the side of the printhead 102, it cannot be determined when an image signal will begin and end. It is therefore required that VH be turned on at a timing considerably earlier than that at which the initial discharge image signal is input to the printhead 102. Further, even after all of the heating pulses have been input to the printhead 102, it is necessary to halt the application of voltage to the printhead 102 in synch with other mechanical control operations, etc.
If VH is applied to the printhead 102 while ink is not being discharged from the printhead, wasteful power consumption will occur. Further, if an image signal rendered erroneous by noise or the like is sent to the printhead 102, control for turning on VH will be delayed.